1. Field of the Invention
The present invention relates to a device for an electrophotographic apparatus and, more specifically, to a device for uniformly regulating the density supplied by the developing unit.
2. Background Art
Supplying a consistently high quality of toner to a photoconductive drum is crucial for the proper operation of an electrophotographic apparatus during the printing process. An electrophotographic apparatus can be either one of a laser printer, an electronic copier, a facsimile machine, or any versatile office machine. The general operation of an electrophotographic apparatus starts with paper being loaded from a supply tray and then transported through to a high pressure transfer roller. The high pressure transfer roller transfers the toner image from the photoconductive drum onto the sheet of paper. Subsequently, the paper is transported to a fixing device that fuses the toner image onto the paper using both heat and pressure rollers.
To prepare the toner image for the high pressure transfer roller, it is necessary to attach toner particles to the latent electrostatic image on the photoconductive drum. The toner particles are applied by the developing unit and transform the latent electrostatic image into a latent toner image.
A toner cartridge charged with a static voltage is contained in the developing unit and supplies toner to the supply roller. The toner is stirred by an agitator that keeps the toner evenly charged and mixed. The electrostatically charged toner is transferred to the supply roller by the rotation of the agitator. The rotation of the supply roller then transfers the toner to a developing roller. The toner deposited on the developing roller is uniformly applied due to a doctor-blade that maintains a constant level of thickness of toner on the developing roller.
A photoconductive drum is charged by a charger roller with a static negative voltage. Then, the photoconductive drum is rotated and exposed to the light from a light emitting device. The parts of the photoconductive drum surface exposed to the light generate an latent electrostatic image. This latent electrostatic image is transformed into a latent toner image when toner particles are attached to the latent electrostatic image by the developing roller. A sheet of paper loaded from a paper tray is fed into the electrophotographic apparatus by a pickup roller. The paper is then transferred to a high pressure transfer roller that presses the paper against the photoconductive drum to transfer the toner image onto the sheet of paper from the drum. Then the paper, and applied toner image, is transported between the heating roller and the pressure roller of a fixing unit to fuse the toner image into the sheet using both heat and pressure.
More specifically, the developing roller is mounted between the photoconductive drum and the toner supply roller. Toner is stirred by the agitator and fed to the developing roller. A doctor-blade contacts the developing roller and controls the thickness of the toner applied to the developing roller. Then, the photoconductive drum rotates and brings the latent electrostatic image into contact with the layer of toner formed on the developing roller, thus developing a latent toner image.
However, since the volume of the toner regulator is fixed, and toner is separately distributed in a flexible area and a stagnant area, it is difficult to uniformly mix the toner. Therefore, it is also difficult to appropriately charge the toner. Moreover, since there is no additional device for controlling the toner supplied to the regulator, if the toner is excessively supplied through the supply channel by the agitator, a background may occur on the image bearing document. Furthermore, the excessive supply of the toner leads to an increase in the pressure of the regulator and thus an increase in internal volume density. Then the toner becomes stagnant and is blocked. Only the uncharged toner or carrier deviate from the doctor blade, thereby deteriorating density and worsening development. Furthermore, a partial blocking at the supply channel is the cause of a white band.
Techniques to improve the development process are shown, for example, in U.S. Pat. No. 5,649,197 to Fujita entitled Development Apparatus Including Nonmagnetic Single-Component Developer Guide Member, U.S. Pat. No. 4,458,627 to Hosono entitled Developing Apparatus for Electrostatic Image, and U.S. Pat. No. 5,722,022 to Park entitled Device for Regulating Thickness of Toner Layer on Developing Roller. Developing units found in the contemporary art do not have a device that allows the toner pressure in the area of the developing roller to stay constant despite the forces generated by the rotation of the agitators in the toner reservoir, that is simple to make, that has an elastic structure, that prevents a toner block from developing in the developer unit, that aids in maintaining uniformly charged toner in the developing roller area, and that improves the quality of images produced by an electrophotographic apparatus.
I believe it may be possible to improve on the prior art by providing a developing unit that has a device that uniformly regulates toner density on the developer roller while maintaining constant pressure in the developing unit despite the rotation of agitators, and that aids in maintaining uniformly charged toner in the developer roller area.